A typical sheet or envelope handling device includes various structures, motors and sensors. For example, a typical envelope handling device includes an envelope feeding structure for feeding an envelope or a batch of envelopes in singular fashion in a downstream path of travel to a work station. Typical envelope handling devices employ ejection rollers or ejection belts operating at a constant speed, or at some speed that varies as a function of time, speeds chosen so as to avoid envelope collisions and noise, and also to avoid so-called bounce-back from a wall when an envelope strikes a wall designed to stop its forward travel and cause it to drop onto the top of a stack. Depending on how the envelope moves through the device, more or less noise and bounce-back will result. It is beneficial to control to a fine degree the motion of a sheet or envelope handling device so as to keep noise and undesirable motion of the sheets or envelopes to a minimum.
The prior art uses motion profiles to express, as a function of time, the velocity/speed of an axis of a motor that causes motion of a sheet in a mailing system. A motion profile consists of a series of segments, each segment having a duration and each corresponding to a state of motion of an axis of a motor ultimately responsible for imparting motion to a sheet or envelope.
For example, a motor may have an axis that in rotating pulls a sheet through part of a mailing system at a certain speed, after accelerating at a specified acceleration as a function of time, and concluding with some specified deceleration as a function of time. If the sheet does not slip, then the motion of the sheet can be correlated precisely with the motion of the axis of the motor: the sheet moves through the mailing system with a speed that is exactly equal to the speed of rotation of the part of the axis in contact with the sheet, i.e. usually the surface of a belt driven by the axis. In this case, commands are sometimes sent to a motor to impart motion to a sheet, for a series of time segments, based simply on the assumption that the motion of the axis of the motor causing the motion of the sheet can be equated to the motion of the sheet.
On occasion, however, a sheet in a sheet handling device will slip so that the motion of the axis does not necessarily indicate the motion of a sheet (or envelope). Then the motion of an axis of a motor can be conditioned based on receiving commands from sensors used to detect the presence of the sheet as it moves through the sheet handling device.
Whether commands are sent based on a sheet not slipping, or based on information from sensors, the commands can be sent without regard to, i.e. independent of, the motion of the axis of any other motor. It is also possible, however, to send commands to a motor based on the motion of other motors.
The sending of commands to a motor based on the motion of (the axis) of another motor (which motion can be based on the motion of still a third motor, and so on), was in the past accomplished using mechanical gearing. Today, motors can be made to communicate electronically and use what is now sometimes referred to as electronic gearing, but also known as displacement mapping, in which the motion of the axis of one motor is expressed in terms depending only on the motion of the axis of another motor, whether or not there is slippage.
For either displacement mapping or sending commands without regard for the motion of any other motor, it is sometimes necessary to have the axis of a motor make a so-called quick step, involving first an acceleration and then a deceleration. Both of these transition segments are called quick steps, and involve sending commands to the axis of a motor so that the axis has a velocity that depends not only on time (i.e. time raised to the first power), but also on time raised to the second power, i.e. the velocity equation is parabolic.
What is needed is a methodology for providing motion profiles that express the required motion of axes of motors for causing a sheet to move through a mailing system in a desired way, a methodology that incorporates, for a given segment of the motion profile, a basis for specifying a particular kind of motion (the kind independent of the motion of other axes in the mailing system, and the kind that depend on the motion of other axes), and that sets out rules by which to construct each possible kind of segment.